This protocol will test the hypnotic efficacy of low-dose (physiological replacement) melatonin for the treatment of age-related insomnia. Each subject will be treated for two-week blocks (in rotation) with placebo and three different melatonin dosing strategies that produce unique pharmacokinetic profiles. Response variables will include measures of sleep, daytime alertness, and circadian phase. On the last night of each treatment arm, subjects will be admitted for pharmacokinetic, temperature sleep & circadian phase assessment.